170. Implementing single-isocenter volumetric modulated arc therapy radiosurgery treatment for multiple intracranial metastases

Abstract

PurposeRecently an increase in radiosurgery treatments for multiple metastases has been observed. Traditionally these lesions were treated using one isocenter for each target and the patient had to be shifted during a single session for repositioning.The implementation of single-isocenter volumetric modulated arc therapy (VMAT) radiosurgery technique for multiple intracranial lesions allows a significant reduction of treatment times, as well as enhancing accuracy by reducing the potential intrafraction motion [1]. MethodsFor 20 patients treated with VMAT for multiple brain metastases we have analyzed the treatment process. Each case had different number and distribution of metastases. We performed a CT simulation scan with 1.25 mm thickness slice for all patients. The simulation images were registered with a MR in order to define the targets. For each case we compared the VMAT single-isocenter technique plan with the sums of the plans of every single lesion. Plans were evaluated using Dose Volume Histograms, Conformity and Uniformity Indexes. All the plans were optimized with 6 MV flattened filter free arcs. Set up checks were performed using both BrainLAB ExacTrac and Varian Cone Beam CT (CBCT). For 10 patients we also evaluated the intrafraction motion. ResultsNo significant difference was detected between the two techniques. The single-isocenter technique comes out better for the dose distributions especially for low doses. We discovered a good agreement between ExacTrac and CBCT and a minimum intrafraction movement (<1 mm) which was dosimetrically insignificant also for peripheral lesions. We underline a very significant reduction of treatment times. ConclusionsBoth methods achieve good dosimetric results. Single-isocenter VMAT radiosurgery treatment for multiple metastases is a faster technique and could be performed safely using image guided radiotherapy treatment thus relieving patient discomfort.